The aims of this proposal are to (1) continue exploration of the cerebellum by examining the raphe pallidus serotonin neurons and their cerebellar projections, (2) develop a new method for tracing transmitter specific pathways utilizing microinjections of 3H-serotonin into the raphe, and (3) develop a strategy for detailed analysis of the central nervous system with neurons of identified transmitter content using quantitative classical and chemospecific methods. The methods used will include morphological procedures such as Golgi and morphometry as well as fluorescence microscopy, 3H-serotonin light and electron microscopic autoradiography, anterograde tracing methods with radioactive amino acids and 3H-serotonin to trace the general and the serotonin specific paths from raphe pallidus to cerebellum, and combined degeneration after electrolytic lesions of raphe and 3H-serotonin autoradiography. The question of synaptic and non-synaptic serotonin connections with respect to specific and nonspecific neuronal innervation will be examined. The existence of reciprocity in the raphe-cerebellum and raphe in a closed feedback system will be investigated.